SAN FRANCISCO - Steve Jobs is back at work at Apple Inc., returning to his job as chief executive officer as planned after taking medical leave in January.

“Steve is back to work,’’ said Steve Dowling, a spokesman at the Cupertino, Calif.-based company. Jobs is at Apple a few days a week and working from home the rest of the time, he said. “We are very glad to have him back.’’

Jobs’s return may reassure investors concerned that he was too sick to continue as CEO, said Gene Munster, an analyst with Piper Jaffray & Co. in Minneapolis. Jobs, a cancer survivor, said in January he would resume his daily duties at the end of June. Jobs’s doctors disclosed last week that he had a liver transplant and said he is recovering well.

“It should give investors confidence in Apple’s three-to-five-year road map,’’ said Munster, who recommends buying the stock and doesn’t own it. “Having Steve Jobs back means they got the visionary back.’’

Dowling declined to say whether Jobs, 54, was at the office yesterday. He also declined to comment on Jobs’s liver transplant or whether the company will provide more information on the CEO’s health.

Jobs had his transplant about two months ago, according to a person familiar with the matter. Jobs was the sickest patient on the waiting list at the time a liver was available, James Eason, chief of transplantation at the Methodist University Hospital, said.

Most liver-transplant patients are back at work in about two to three months, Abhinav Humar, clinical director of the Division of Transplantation at the University of Pittsburgh Medical Center, said.

Jobs, who cofounded Apple in 1976 with Steve Wozniak, appeared thinner at the company’s developers conference in June 2008, sparking speculation he was ill. Apple first said he was suffering from a “common bug’’ and then declined to comment, saying his health was a private matter. The shares fluctuated with each new report on Jobs’s health.

On Jan. 5, Jobs said he would remain CEO while seeking a “relatively simple’’ treatment for a nutritional ailment. Nine days later, Jobs said he had decided to take himself “out of the limelight’’ and go on leave after learning his health issues were more complex than he originally thought.

Those disclosures bothered some corporate governance experts, who said Apple and its board should have been more forthcoming with information on Jobs’s health. Jobs’s January statements may be a sign the board is aware of those concerns, said Ryan Jacob, head of the Jacob Internet Fund in Los Angeles, which owns Apple shares.

“The impression was there, prior to January, that the board didn’t have a complete handle on the condition of the CEO and that was troubling because, as an investor, I count on the board to represent my interests,’’ Jacob said

Operating chief Tim Cook was in charge of day-to-day operations while Jobs was on leave.